In order to surgically place a threaded dental implant, a pilot hole is drilled into the bone in which the implant will be placed. Successively larger diameter drill bits are then used to increase the hole to the minor diameter of the threaded implant. A screw tap is then used to form a thread pattern in the bone forming the walls of the bore.
To eliminate the need for a separate tapping step prior to implantation, self-tapping screw implants have been developed. EP 0 237 505 to Jorneus discloses a screw shaped anchoring implant with cavities formed from two mutually perpendicular through holes which are also perpendicular to the longitudinal axis of the implant or by three cavities formed on the outer, circular surface of the implant so that the cutting edges have a positive cutting angle.
U.S. Pat. No. 5,269,685 to Jorneus et al. describes a screw-shaped titanium anchoring member comprising at least one cavity located at the forward tip of the screw. The edges of the cavity form a cutting surface. A clearance is provided behind the cutting edges. The clearance is provided by slightly beveling the outer surface behind the cutting edge.
Restore.TM., a self-tapping screw implant manufactured by Lifecore Biomedical, Inc., has four chip cavities formed on the outer surface of the dental implant so that the cutting surfaces form a zero rake angle.
Other self-tapping screw implants are also commercially available.
In spite of the utility of self-tapping implants, it can be difficult, in particular in dense cortical bone, to seat self-tapping screw implants. Self-tapping implants for dense bone must have excellent cutting characteristics to avoid damaging the implant and/or the surrounding bone.
It is a goal of the present invention to provide a self-tapping screw type dental implant which will provide excellent tapping ability into dense bone such as Type 1 (D1), (Misch CE: Contemporary Implant Density, 1993).